MEMS based actuators are enabling the emergence of a host of new components for use in displays, inertial measurement systems, RF and wireless systems and fiber-optic. In particular, optical components that are more compact, highly reliable, low power consumption and low cost are highly desirable. Examples of such components include switches, variable optical attenuators (VOA), tunable filters, and wavelength blockers.
One particularly important class of MEMS devices for such applications is the MEMS Micromirror rotating around a torsional hinge. In the early work on such devices the actuation was based on parallel plate electrostatic force usually between the mirror and another electrode on one side of the axis. Some variations in this line are discussed by Miller (U.S. Pat. No. 7,010,188) and Nasiri (U.S. Pat. No. 6,533,947). More recent developments in the field include vertical comb drive actuators, which are discussed by Costello (U.S. Pat. Nos. 6,838,738; 6,628,856 and 6,782,153) and Novotny (U.S. Pat. Nos. 6,751,395; 6,914,711 and 6,914,710).
Combs drive actuation exhibit significant advantages over parallel plate actuation in the areas of speed, actuation voltage, and range of motion. Commercial examples include VOA products from Lightconnect (now Neophotonics), Dicon Fiberoptics and Santec.
Notwithstanding these advantages, there are limitations in the approaches of Costello, Novotny and others. Some of the limitations are in the actuation mechanism, the functional design space and the fabrication process of MEMS with a structure rotating around a torsional hinge. For example, the reduction of the amount of force and the throw distance are limited as in the use of fringe field in Costello's approach. In particular, the actuation mechanism of parallel plate force cannot be added. Furthermore, the comb fingers have to be like cantilevers and the fingers structure cannot be mechanically closed. Therefore, the comb fingers cannot be too long as they become susceptible to lateral snap. Similarly, in the case of Novotny, again, parallel plate force cannot be added and the stator combs can only be on one side of the structure. This will affect the air damping on the two sides of the structure axis and lead to higher susceptibility to mechanical shock.
MEMS with a structure rotating around a torsional hinge, such as micromirrors, are often operated close to the snapping point and the design and performance of such devices especially for low voltage and high stability applications is desired. This patent application presents a MEMS that combines both comb actuation with parallel plate force actuation to provide the maximum rotational force or torque and the design of MEMS that allows for snapping between the stator and rotor structures. Furthermore, this patent application presents a MEMS that recovers properly when the applied voltage is eliminated, or reduced below a certain operating voltage threshold thus overcoming many of the limitations of the prior art.